1. Technical Field
The present invention relates to an optical module for an atomic oscillator and an atomic oscillator.
2. Related art
In recent years, an atomic oscillator using CPT (Coherent Population Trapping) as one of quantum interference effects is proposed, and miniaturization of an apparatus and reduction in power consumption are expected. The atomic oscillator using the CPT is the oscillator using a phenomenon (EIT phenomenon: Electromagnetically Induced Transparency) in which when two resonant lights having wavelengths (frequencies) different from each other are simultaneously irradiated to an alkali metal atom, the absorption of the two resonant lights is stopped. For example, JP-A-2009-89116 (patent document 1) discloses an atomic oscillator using CPT, which includes an optical module including a light source to emit coherent light, a gas cell in which alkali metal atoms are enclosed, and a light-receiving element to detect the intensity of light passing through the gas cell.
In the atomic oscillator using the CPT, for example, a semiconductor laser is used as a light source. In the atomic oscillator using the semiconductor laser as the light source, for example, the drive current of the semiconductor laser is modulated so that a sideband wave is generated in the light emitted from the semiconductor laser and the EIT phenomenon is caused.
However, the light emitted from the semiconductor laser in which the drive current is modulated includes not only the sideband wave but also a fundamental wave (carrier wave) which does not contribute to the EIT phenomenon and has a center wavelength. When the fundamental wave is irradiated to the alkali metal atom, there is a case where the wavelength (frequency) of light absorbed by the alkali metal atom is changed (AC Stark effect), and the stability of frequency of the atomic oscillator is reduced.